With regard to an external auditory canal insertion type earphone used by inserting a receiver into an external auditory canal, a sealed type and an open type exist. The sealed type causes the external auditory canal to be in a sealed state by an ear tip mounted on the tip of the receiver. The open type creates an open state (non-sealed state) as a result of having a connection between outside space and the external auditory canal by a vent hole formed on the ear tip.
For example, Patent Literature 1 proposes a conventional open type earphone having a vent hole formed on an ear tip. FIG. 16 shows a conventional earphone 200 disclosed in Patent Literature 1. In FIG. 16, (a) is a plan view of the earphone 200, and (b) is a cross sectional view along line A-O-B in the earphone 200 shown in (a). Sound waves generated by a loudspeaker unit 201 are released in an external auditory canal via a sound hole 204 formed on a sound conduit tube 202. The sound waves released in the external auditory canal are separated into sound waves that propagate to the eardrum and sound waves that leak to outside space from vent holes 205 formed on an ear tip 203.